The unique plants with particularly powerful stinks that mimic the smell of decaying flesh and poop have captivated researchers and flower lovers since time immemorial. The most notorious of these is the Asian skunk cabbage (Symplocarpus renifolius), which releases a particularly foul-smelling odor. This unique smell, largely due to emission of dimethyl disulfide, lures the flies in to pollinate. This remarkable phenomenon is a great reminder of an extraordinary evolutionary adaptation.
Researchers have discovered that Symplocarpus renifolius developed its fetid aroma through only two amino acid swaps in its genetic makeup. Surprisingly, this is not an exception to the rule of one in the plant world. In fact, many unrelated species have independently evolved to produce these stinkening smells — making for an incredibly stinky, but cool, case of convergent evolution. Foul smelling plants are the genus Eurya, such as E. japonica, and genus Asarum, including A. simile. We can’t skip the famous stinking glad, known as skunk cabbage!
The chemical dimethyl disulfide is so stinky it’s considered a marker of environmental health crises, its odor likened to that of decaying animal bodies or excrement. This compound serves two important functions. This not only drives away would-be herbivores, but it draws in pollinators that prefer the smell of death, particularly flies. The development and retention of this scent is essential for the reproductive fitness of these plants.
In an intriguing twist, research has shown that the Asarum species has gained and lost the ability to produce dimethyl disulfide more than 18 times throughout its evolutionary history. While beautiful, this fluctuation serves to illustrate evolution and adaptation’s constantly shifting landscape. At the same time, research has shown that in parallel fashion, three different plant lineages have evolved the same fetid stink through many independent genetic changes. These events remind us of the labyrinthine routes an evolutionary trajectory can take and the unexpected ways in which disparate organisms can be connected.
Here at the heart of this evolutionary phenomenon is a gene called SBP1, which experienced a gene duplication. This redundancy has enabled the evolution of other enzymes to connect two methanethiol molecules to create dimethyl disulfide. Methanethiol is already famous enough on its own account, being responsible for human halitosis, aka bad breath.
In contrast, for more distantly related species such as Asarum simile and Eurya japonica, developing the signature stinky smell took three discrete genetic changes. These new buildings are a testament to the incredible resiliency of these plants. It’s a story that showcases the power of gene duplication in evolution—a process that plants, along with many other organisms, including humans, have experienced multiple times.
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